Effects Of Biochar Application On Physiology,Growth And Water And Fertilizer Utilization Of Cotton Under Drip Irrigation

Object:To explore the effect of applying biochar on the physiology and growth of cotton under drip irrigation and the utilization of water and fertilizer,through two-year test in field under mulched drip irrigation,to explore the effect of different biochar application times（before and after the freeze-thaw period）and biochar application amounts on soil hydrothermal conditions,cotton physiology and growth,cotton yield,fiber quality and the utilization efficiency of water and fertilizer in the mulched drip-irrigated cotton field in northern Xinjiang.Methods:Our experiment set up two biochar application times（pre-freeze-thaw 2020.10.27,post-freeze-thaw 2021.4.16）,four biochar application rates（0.33%,0.66%,1.00%,1.33%of soil mass fraction）and one control check without biochar application,a total of 9 treatments.We selected cotton straw biochar,and mixed the biochar evenly with 0—40 cm soil layer by means of tillage and rotary tillage.Results:（1）The application of biochar increased the topsoil porosity and reduced the bulk density.With the increase of biochar application,the influence of biochar on bulk density and porosity increased.There was no significant difference between the application of biochar before and after freeze-thaw.The application of biochar increased the soil volume water content,which decreased first and then increased with the increase of biochar application.The application of biochar after freezing was slightly better than that before freezing.Applying biochar reduced the water consumption of cotton during the growth period,and the water consumption decreased first and then increased with the increase of biochar application.The water consumption of biochar application after freezing was lower than that of biochar application before freezing.（2）The application of biochar increased the temperature of the topsoil and the effective accumulated temperature of the soil.The increasing effect first increased and then decreased with the increase of the amount of biochar applied.The application of biochar after freeze-thaw was fractionally better than that before freeze-thaw.The application of biochar increased the content of nitrate nitrogen,ammonium nitrogen and available phosphorus in soil,which increased with the increase of biochar application.（3）The application of biochar increased the plant height,stem diameter,leaf area index and dry matter accumulation of cotton,and each index increased first and then decreased with the increase of biochar application.The application of biochar increased the net photosynthetic rate,transpiration rate and stomatal conductance of cotton leaves,and decreased the intercellular CO₂ concentration.With the increase of biochar application,the change range of each index showed a trend of first increasing and then decreasing.The application of biochar before and after freeze-thaw had no significant effect on the physiological growth index of cotton,and the application of biochar after freezing was slightly better than that before freezing.（4）Applying biochar increased the yield,lint percentage,water use efficiency,irrigation water productivity and fertilizer partial productivity of seed cotton,but had no regular effect on the effective boll number per plant and boll weight per plant.After freezing,the maximum yield was obtained by applying biochar at the rate of 0.66%of soil mass fraction,13.18%and 14.08%higher than that without biochar application in two years.The application of biochar increased the fiber length,uniformity index and breaking strength of cotton without affecting the elongation,and improved the cotton quality grade based on micronaire value.（5）A comprehensive evaluation based on entropy weight-TOPSIS method was conducted on the soil index and cotton index of drip irrigation.The results showed that the application of 0.66%biochar after freeze-thaw improved the soil physical and chemical properties,physiology and growth,yield and quality of drip irrigation cotton,and water and fertilizer utilization efficiency to the greatest extent.The improvement effect of applying biochar after freeze-thaw was better than that before freeze-thaw.The comprehensive improvement effect first increased and then decreased with the increase of biochar application.The one-year aging of biochar in the field kept the improvement effect,reflecting the sustainability of biochar’s improvement.Conclusion:To sum up,the improvement effect of applying biochar after freezing is better than that before freezing.The improvement effect of drip irrigation cotton field soil and drip irrigation cotton generally shows a trend of first increasing and then decreasing.After the freeze-thaw period,the best improvement effect is achieved by applying biochar at 0.66%of soil mass fraction.